Re: [TCML] Caps

[Gary Lau <glau1024@xxxxxxxxx>]

First let's clear up the mundane - The term is "resonant rise".

The reason for using an LTR cap is to allow the maximum power to be pulled
from the NST.  The underlying analysis  is complex but the fact is that the
most power will be processed (correlating to maximum spark length) when
using an LTR cap.  I performed an experiment to measure the power processed
for a variety of cap sizes with a 15/30 and 15/60 NST, and LTR was the
clear winner.  See
https://docs.google.com/open?id=0B0afsm3K5nFYNGQ3MmJlZGEtYjQ5My00OTJhLTkwNDMtOWEwMjRkYWJkZjAy

The other thing is that spark length is correlated with bang size, not
simply power.  Given that the bang voltage is (or should be) constant for
all cap sizes, the bang size (.5*C*V**2) is proportional to cap size.
So while having a large cap will get you the maximum spark length, it's
also true that said longer sparks won't be as bright as those generated by
a smaller cap.  So the choice depends of what your goal is.

As far as what's safer to use to prevent blowing out stuff, using
deliberately non-mains-resonant caps will *somewhat* idiot proof the
setting of the safety gaps.  But assuming that the main and safety gaps are
properly set, using STR or LRT or mains-resonant caps are all equally
stressful.

Regards, Gary Lau
MA, USA

On Wed, Aug 29, 2012 at 2:22 AM, Christian Hill <monolegal@xxxxxxxxx> wrote:

> Hello. I am building my first coil and have a few questions. I read that
> you should stay away from using a resonate sized capacitor as it can cause
> a "condition called resonate rise." Multiple sources say to use a "larger
> that resonate" capacitor to keep this from happening. I've read that you
> can also use a multiple of the LTR capacitance value as well. Let's say
> that the optimum LTR capacitance is 10nF. Since I can double it and use
> 20nF would I also be able to half it and use 5nF? (Assuming that my voltage
> needs were met, of course).
>
> I would assume that the closer I get to the resonate capacitance value, the
> better chances of resonate rise I have. So I should stay as close as
> possible to a multiple of the LTR capacitance, correct? Or should I just
> meet my voltage needs, tune the coil accordingly, and make use of safety
> gaps?
>
> I am asking all of these capacitor questions because I want to get the most
> out of my money. Those Cornell-Dubillier 942C20P15K-F's can really add up
> when you're on a budget. I tried searching through the archives and have
> poured over dozens of tesla coil guides but found nothing that really
> answered my questions. Thank you very much for your help.
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